1. Field of the Invention
The present invention relates to an electric motor.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication No. H10-285871 discloses a motor actuator, which drives an air flow passage switching door of an air conditioning system of a vehicle. In an electric motor, which is used as a drive source of the motor actuator, a bearing is fixed in an interior of a tubular bearing receiver formed in a housing of the motor and rotatably supports a rotatable shaft. A distal end section of the rotatable shaft projects outward from an opening of the bearing receiver to an outside of the housing. A speed reducing gear, which reduces a rotational speed of the rotatable shaft in corporation with an external gear, is fixed to the distal end section of the rotatable shaft.
In the above motor, due to a viscosity of a lubricant (e.g., a grease), the lubricant is adhered to an outer end surface of the bearing, which is exposed from the opening of the bearing receiver. Thereby, the lubricant is thoroughly applied between the bearing and the rotatable shaft to improve the lubricity of the bearing, so that the noise of the motor and of the entire motor actuator can be reduced. However, in the above motor, due to a reduction in the viscosity of the lubricant under the high temperature state or due to a centrifugal force of the rotatable shaft, the lubricant, which is applied to the bearing, may possibly flow out to the outside of the housing, thereby resulting in generation of a noise caused by the rotational friction.